This application is based upon and claims the benefit of the priorities from the prior Japanese Patent Applications No. 2001-259310 filed on or around Aug. 29, 2001 and No. 2001-298252 filed on or around Sep. 27, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The invention relates to a semiconductor device and a method of manufacturing the same, and more particularly relates to a semiconductor device including a bump electrode provided on an electrode via an under bump metal film, and a method of manufacturing such a semiconductor device. Further, the invention relates to a semiconductor device in which substrates are joined, semiconductor substrates are joined, and the substrate and the semiconductor substrate are joined, and a method of manufacturing such a semiconductor device.
2. Description of the Related Art
As semiconductor chips constituting semiconductor devices are being highly integrated and improved in their functions, a variety of methods have been developed and applied in order to connect external connection electrodes (i.e. bonding pads) of the semiconductor chips to electrodes of a wiring substrate (i.e. a printed circuit board) on which the semiconductor chips are mounted. There have been strong demands for highly integrated semiconductor chips such as IC (integrated circuit) chips and LSI (large scale integrated circuit) chips to be compatible with high speed circuit operation, efficient heat diffusion, and accommodation of multiple terminals (pins). Recently, it is anticipated that high-end semiconductor chips are required to have several thousands of external connection electrodes (terminals).
Further, semiconductor devices have been required to be compact in size and light in weight, and to perform multiple functions in the view of a system side. In order to satisfy the foregoing requirements, it is inevitable to mount semiconductor chips in an extensively integrated state on the wiring substrate. A multiple chip structure or a three-dimensional mounting structure is being studied in order to meet requirements for multiple functions.
The flip chip (FC) method or tape-automated bonding method (TAB) using bump electrodes is advantageous in order to increase terminals. In the FC method, bump electrodes are provided at least at either external connection electrodes of the semiconductor chip or electrodes of the wiring substrate, and the bump electrodes and electrodes are connected, or the bump electrodes are mutually connected. For instance, in a semiconductor chip having an extremely large number of high-end terminals, a plurality of solder bump electrodes are arranged in the shape of a lattice on a surface (circuit mounding surface) of the semiconductor chip. The semiconductor chip is faced with a surface of the wiring substrate, and is mounted thereon. Thereafter, solder reflow is performed in order to join soldering bump electrodes and the wiring substrate, so that the semiconductor chip is mounted on the wiring substrate.
In the case of the TAB method, gold (Au) bump electrodes are provided on external connection terminals of the semiconductor chip, and copper (Cu)/tin (Sn) bump electrodes are formed on electrodes of the wiring substrate. Thereafter, the bump electrodes are positioned with respect to leads of the wiring substrate, and the Au bump electrodes are joined to the Sn/Cu bump electrodes by full thermo-compression. In this state, the semiconductor chips are completely mounted on the wiring substrate.
Minute bump electrodes are usually made by a plating process, as shown in FIG. 15(A) to FIG. 15(D) of the accompanying drawings.
(1) First of all, a semiconductor wafer 100 is prepared (see FIG. 15(A)). The semiconductor wafer 100 is in a state prior to the dicing into semiconductor chips. An external connection electrode (bonding pad) 101 is provided on the semiconductor wafer 100 at a position where a semiconductor chip is to be formed. A passivation film 102 is present on the external connection electrode 101, and has an aperture 102H. A polyimide group resin film 103 extends over a bump electrode forming region on the passivation film 102, and has an aperture 103H.
(2) An under bump metal (UBM) film 110 is formed all over the semiconductor wafer 100, i.e. on the polyimide group resin film 103, passivation film 102, an inner wall of the aperture 103H, an inner wall of the aperture 102H, and the external connection electrode 101 which is exposed from the apertures 103H and 102H. The UBM film 110 is applied by the sputtering, plating or the like, and is required to perform the following.
(a) To keep the external connection electrode 101 and Au bump electrode 112 (see FIG. 15(B)) electrically conductive;
(b) To keep the external connection electrode 101 and bump electrode 112 in close contact with each other;
(c) To function as a barrier for preventing heat diffusion between the external connection electrode 101 and the bump electrode 112, and preventing reduced conduction and adhesion depending upon time; and
(d) To function as a feeding layer during the plating.
In order to meet these requirements, the UBM film 110 includes two or three stacked layers. For instance, the UBM film 110 is constituted by a titanium (Ti) layer, a nickel (Ni) layer and a palladium (Pd) layer which are stacked one over after another, or a chromium (Cr) layer, a Cu layer and an Au layer which are stacked one over after another, when observed from the external connection electrode 101 to the bump electrode. Further, the UBM film 110 is required to be several hundred nm to several xcexcm thick.
(3) A photoresist film is applied onto the UBM film 110, and is exposed and developed by the photolithography process. A bump electrode-forming mask 111 is made using the photoresist film (refer to FIG. 15(B)). The mask 111 has an aperture 111H via which the UMB film 110 has its surface exposed on the external connection electrode 101.
(4) Electricity is supplied to the UBM film 110 by the electrolytic plating, so that the Au bump electrode 112 is formed on the UBM film 110 in the aperture 111H of the bump electrode-forming mask 111. Refer to FIG. 15(B).
(5) Thereafter, the bump electrode-forming mask 111 is stripped as shown in FIG. 15(C).
(6) The UBM film 110 is etched using the Au bump electrode 112 as an etching mask, and has its unnecessary part removed. For instance, when the UBM film 110 is constituted by the Ti, Ni and Pd layers, the Pd and Ni layers are wet-etched using a composite solution containing nitric acid, hydrochloric acid and acetic acid. Thereafter, the Ti layer is wet-etched using a fluoride acid solution.
A solder bump electrode made of lead (Pb)xe2x80x94Sn, silver (Ag)xe2x80x94Sn or the like are manufactured as shown in FIG. 16(A) to FIG. 16(E).
(1) First of all, a semiconductor wafer 100 is prepared as shown in FIG. 16(A), similarly to the foregoing Au bump electrode 112. An external connection electrode 101 is provided over a semiconductor chip forming regions of the semiconductor wafer 100. A passivation film 102 having an aperture 102H, and a polyimide group resin film 103 having an aperture 103H are formed over the external connection electrode 101.
(2) Referring to FIG. 16(A), a UBM film 110 is formed on the semiconductor wafer 100 and the external connection electrode 101. This UBM film 110 has the stacked structure similarly to the Au bump electrode 112. However, the UBM film 110 is thicker the UBM film 110 in the foregoing case in order to prevent diffusion of Sn from a solder bump electrode 122 to the external connection electrode 101.
(3) Thereafter, a bump electrode-forming mask 121 is formed on the UBM film 110 using the photolithography process (refer to FIG. 16(B)). The bump electrode-forming mask 121 has an aperture 121H via which the front surface of the UBM film 110 is exposed on the external connection electrode 101.
(4) Electricity is supplied to the UBM film 110 by the electrolytic plating process. Referring to FIG. 16(B), the solder bump electrode 122 is formed in an aperture 121H of the bump electrode-forming mask 121 and on the UBM film 110.
(5) The bump electrode-forming mask 121 is stripped as shown in FIG. 16(C).
(6) Referring to FIG. 16(D), the UBM film 110 is wet-etched using the solder bump electrode 122 as an etching mask, and has its unnecessary part removed.
(7) Solder reflowing is performed in order to form a spherical solder bump electrode 122B, as shown in FIG. 16(E).
The semiconductor devices including the Au bump electrode 112 and the solder bump electrode 122 seem to have the following problems.
(1) When making the Au bump electrode 112, the UBM film 110 is wet-etched in order to remove its unnecessary part. Since the wet-etching process is generally isotropic, undercuts 110U are caused just under the Au bump electrode 112, as shown by dotted lines in FIG. 17. For instance, when the semiconductor wafer 100 has an 8-inch diameter, each undercut 110U may be approximately 10 xcexcm wide. It is assumed here that the Au bump electrode 112 has a diameter which is equal to or less than 20 xcexcm. In such a case, the UBM film 110 is lessened by the undercuts 110U, so that no junction can be formed between the external connection electrode 101 and the Au bump electrode 112. This problem also occurs when manufacturing the solder bump electrode 122.
(2) It is very difficult to make a minute Au bump electrode 112 or solder bump electrode 122. Therefore, it is also very difficult for a semiconductor device to accelerate circuit operation, promote heat diffusion, increase the number of terminals, be compact in size and light in weight, and perform multiple functions.
(3) Either the Au bump electrode 112 or the solder bump electrode 122 may be joined with reduced mechanical strength because of the undercuts 110U of the UBM film 110. As a result, the joined portion may be cracked and broken due to stress resulting from a temperature cycle, which will lead to reduced reliability of the semiconductor device.
(4) It is conceivable to adopt a dry etching process or the anisotropic etching such as the reactive ion etching (RIE) process in order to remove the unnecessary part of the UBM film 110. However, the UBM film 110 includes materials which are difficult to dry-etch. If the dry etching process is forcibly applied, the UBM fill 110 has to be etched for a long period of time and at an increased cost.
On the other hand, it is very difficult to join electrodes, which are spaced with a reduced pitch therebetween, using the foregoing solder bump electrodes 122. Specifically, the solder bump electrodes 122 are melted once by the solder reflowing and then hardened in order to join the electrodes. It is difficult to control the shape of joined solder bump electrodes 122. Further, solder bump electrodes 122 tend to expand at sides where they are in contact with adjacent electrodes.
In order to overcome this problem, there is a recent trend to join electrodes in a semiconductor device without using solder bump electrodes. Referring to FIG. 18, an external connection electrode 201 of a semiconductor chip 200 is joined to an external connection electrode 211 of a semiconductor chip 210 without using a solder bump electrode. In other words, the external connection electrodes 201 and 211 are compressed and are joined. Prior to compression, the parallelism (an inclination from the x-y plane) of the semiconductor chips 200 and 210 is adjusted in order that the external connection electrodes 201 and 211 are aligned and have equal deviation of a rotation angle xcex8 in the directions x and y and around the axis z.
Further, when the external connection electrodes 201 and 211 are made of metal such as Cu that easily generates compounds such as oxide or sulfide and so on, it is technically important to reliably join the external connection electrodes 201 and 211 without generating such compounds or to join them via their fresh surfaces after removing such compounds.
In a first method of overcoming the foregoing problem, electrodes may be joined in a hydrogen-reduced atmosphere. In this case, it is necessary to use a joining unit which can adjust the hydrogen-reduced atmosphere to a predetermined pressure and the parallelism of the semiconductor chips 200 and 210, align the external connection electrodes 201 and 211 in the unit of xcexcm, control pressure to be applied, and promote heat for reduction reaction. Heating up to 450xc2x0 C. is necessary for the reduction reaction.
The foregoing joining unit is very bulky and expensive, which means that semiconductor devices manufactured thereby will become also expensive.
There is a second method of overcoming the foregoing problem. In this method, the external connection electrodes 201 and 211 are irradiated by ions at the substantially room temperature and in extremely high vacuum in order to remove oxide or organic substances. Thereafter, the external connection electrodes 201 and 211 are joined. In the second method, it is also necessary to use a joining unit which can completely remove air from a space around the external connection electrodes 201 and 211, radiate ions onto them, adjust the parallelism of the semiconductor chips 200 and 210, align the external connection electrodes 201 and 211 in the unit of xcexcm, control pressure to be applied. Heating up to 450xc2x0 C. is necessary for the reduction reaction.
According to a first aspect of the invention, there is provided a semiconductor device comprising: a first electrode formed above a first substrate; an under bump metal film on the first electrode, the under bump metal film being in the shape of a recess; and a bump electrode embedded in the under bump metal film, the bump electrode having sides and bottom thereof surrounded by the under bump metal film.
The invention provides, as a second aspect, a method of manufacturing a semiconductor device, comprising: forming an electrode; forming an insulating film on the electrode, the insulating film having an aperture; forming an under bump metal film on the insulating film, an inner wall of the aperture and the electrode in the aperture; forming a bump electrode film on the under bump metal film, and embedding the bump electrode film in the aperture; removing the bump electrode film and the under bump metal film from portions except for the aperture to form a bump electrode; and taking off at least a part of a surface of the insulating film.
According to a third aspect of the invention, there is provided a method of manufacturing a semiconductor device, comprising: forming a first substrate having a first electrode; forming a second substrate having a second electrode; applying a non-activated solvent onto a surface of at least one of the first and second electrodes; bringing the second electrode into contact with the first electrode via the non-activated solvent, and compressing the first and second electrodes; and activating the solvent at a temperature which is lower than a melting point temperatures of the first and second electrodes, before the first and second electrodes are joined.
In accordance with a fourth aspect of the invention, there is provided a method of manufacturing a semiconductor device, comprising: forming a first substrate having a first electrode; forming a second substrate having a second electrode; applying a non-activated solvent onto a surface of at least one of the first and second electrodes, the non-activated solvent being heat-cured and being activated at a temperature which is lower than a thermosetting temperature; bringing the second electrode into contact with the first electrode via the non-activated solvent, and compressing the first and second electrodes; activating the solvent at a temperature which is lower than a melting point temperatures of the first and second electrodes, before the first and second electrodes are joined; and heat-curing the solvent after the first and second electrodes are joined.